U.S. Pat. No. 3,692,255 (Von Behren) discloses a magnetic recording tape cartridge for storing data wherein the tape is driven by a pretensioned belt. The specific embodiment of the patent employs magnetic recording tape which is 25 micrometers in thickness. The use of thinner tape has sometimes resulted in excessive variations in tape speed.
It was discovered that the excessive variations in tape speed resulted whenever the following two conditions occurred simultaneously: (1) the tension on the wound tape substantially exceeded the unwinding tension and (2) the tape tended to stick to the underlying convolution so that the windup tension was being released spasmodically. Under the worst conditions, there would be an audible "popping" noise as the tape was unwound.
It is not known whether tape drives other than belt-driven tapes involve this problem. While the belt of the Von Behren patent holds each convolution of recording tape tightly against the underlying convolution, the outer convolutions on an unbelted spool have more freedom to move circumferentially and thus to release windup tensions gradually before being unwound from the spool. Nevertheless, the continuing trend to thinner magnetic recording tapes increases the likelihood that the problem may also occur in other types of drives without anyone being aware of it.